K Series Cooling Mod - issues arising from?

[glasgow]

Ed, Here is the update after spending a few hours in the garage:

 

- Step 1: opened the expansion bottle cap: no change in the coolant level either before or after I opened the cap. No evidence of overpressure inside the bottle (i.e no hissing sound when opened)

 

- Step 2: turned engine on: after about two minutes, coolant level started to gradually increase. Coolant level increased by about 4 cm. Engine temp reached about 85 (on temp gauge), fan cuts in then out- all at idle.

 

- Step 3: Turned the engine off: as soon as I turned the engine off the coolant level rapidly increased followed by a big air bubble and a small amount of coolant overspilled from the bottle.

 

- Step 4: Waited until the engine cooled down: fluid level back to roughly the same normal level.

 

- Step 5: Turned engine on again (engine cold and expansion cap off): coolant level started to gradually increase. Coolant level increased by about 4 cm. Engine temp reached about 85 (on temp gauge), fan cuts in. Turned the engine off, no big air bubble this time and no overspilling of coolant. Waited a few seconds the turned engine on and started reving the engine. Coolant level goes slightly up and down. But, when I looked at the inside of the expansion bottle, while reving the engine, I noticed there are small air bubbles going into the expansion bottle every 1-2 minutes and mainly with the reving. Turned the engine off a few times, no more big air bubble.

 

- Step 6: Waited until the engine cooled down: fluid level back to roughly the same normal level. Then I repeated step 4 and 5 for a couple of more times and same result (no more big bubble but a small air bubbles every 1-2 minutes when reving the engine)

 

- Step 7: Waited until the engine cooled down. Put the bottle cap back on and turned the engine until fan cuts in: coolant risen by about 10mm in the expansion tank (i noticed you Ed had about 5mm rise)

 

Other observations: temp is stable, no signs of oil/water contamination and no fluid leak from clamps site.

 

Questions:

A) are those small air bubbles normal findings OR a sign of early head gasket failure?

 

B) If those small air bubbles a sign of early gasket failure, is it better to go back to the original coolant circuit in order to allow the bubble to be released and not trapped into the system

 

C) finally, I hope there is no harm in running the engine with the expansion cap off (I don’t mean driving but just running and reving the engine)

 

N.B.: I am not sure if the big air bubble I had was a result of airlock during coolant filling last month or due to gradual collection of trapped small air bubbles – it may be worth repeating the experiment in a couple of weeks and see if I get another big bubble.

 

Thanks

[oldbutnotslow]

Glasgow

I am afraid that this sounds very much like HGF to me. ☹️

[Ed W]

My results this morning having left everything alone overnight:

 

No pressure in expansion tank.

Coolant level back to where it started.

No air in radiator.

 

On this info I could suggest that Richards and Charlie's hypothesis is correct, I.e. that the "issue" was bring caused by releasing the pressure whilst hot resulting in localised boiling.

 

This hypothesis could be expanded:

Because there is air in the closed system (in the expansion tank) when the system is hot and pressurised air will become dissolved into the coolant. On boiling the dissolved air will separate from the steam, resulting in air pockets, which then migrate to the nearest highest point, I.e. the top of the radiator. This could explain small quantities of air in the radiator?- Comments please!

 

Ed

[charlie_pank]

Now that is clutching at straws. Air is less soluble in water as temperature increases. here

 

 

[Ed W]

Charlie

 

Thank you! That is what I love about this forum there is always some who has the correct answer

 

Ed

[Ed W]

Further update.

 

I have found a very small weep from the bracket at the front of water rail. So I shall fix this and see is this is the source of the air.

 

Ed

[Stationary M25 Traveller]

Good news !

[Birkin S3 ZA.]

well done Ed hope it works 😬

 

 

[oldbutnotslow]

Update following Zolder track day

 

I kept a close eye on the header tank during the recent Zolder track day, having put back the plumbing to the original lay out.

 

The temperature remained rock steady at 80 degrees with no movement of coolant either into or from the expansion tank at any time during the day of afterward

 

The ambient temperature was 27 degrees and the car was being well ragged so if there were to have been an issue it would most certainly have shown up under these stressed driving conditions.

 

I will certainly not be experimenting again.

 

Anyone want to buy a straight alloy bottom hose connector and 16mm T piece???

 

Grant

[Graham D]

I made the cooling modification over the winter and so far I’ve had no issues at all. In addition the 88 deg thermostat was changed for an 82. As a result the engine runs cooler under normal road conditions and the tendency for the cooling fan to come on in heavy traffic and when parking the car has gone completely - so far.

It’s worth noting that my car has 140 bhp at best and is only used on the road.

 

Graham